Accepted Manuscript

Adsorption studies on the removal of hexavalent chromium from aqueous sol‐

ution using a low cost fertilizer industry waste material

Vinod K. Gupta, Arshi Rastogi, Arunima Nayak

PII: S0021-9797(09)01280-6

DOI: 10.1016/j.jcis.2009.09.065

Reference: YJCIS 15297

To appear in: Journal of Colloid and Interface Science

Received Date: 18 August 2009

Accepted Date: 30 September 2009

Please cite this article as: V.K. Gupta, A. Rastogi, A. Nayak, Adsorption studies on the removal of hexavalent

chromium from aqueous solution using a low cost fertilizer industry waste material, Journal of Colloid and Interface

Science (2009), doi: 10.1016/j.jcis.2009.09.065

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers

we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and

review of the resulting proof before it is published in its final form. Please note that during the production process

errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

1

Adsorption studies on the removal of hexavalent chromium from aqueous solution using a low cost fertilizer industry waste material

Vinod K. Guptaa , Arshi Rastogib, Arunima Nayaka aDepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India KFUPM Chair Professor, King Fahd University of Petroleum and

Minerals, Dhahran, Saudi Arbia (From Jan 2010) b Chemistry Department, K.L.D.A.V.(P.G.) College, Roorkee, India Corresponding Author; E-mail: vinodfcy@iitr.ernet.in, Tel.: +91-1332-285801, Fax:

+91-1332-273560

ACCEPTED MANUSCRIPT

2

Abstract

Low cost fertilizer industry waste material called carbon slurry, produced in

generators of fuel oil based industrial generators was converted into an effective and

efficient adsorbent for the removal of hexavalent chromium (VI) from aqueous solutions.

The waste was chemically treated, activated, characterized and used for the adsorption of

chromium. The work involves batch experiments to investigate the effect of contact time,

pH, temperature, concentration and adsorbent dose on the extent of adsorption by carbon

slurry. The maximum adsorption was found at 70 min., 2.0 pH, 4.0 g/L dose, 303 K

temperature. Maximum adsorption capacity (15.24 mg/g) of Cr(VI) on carbon slurry was

observed at 100 mg/L initial Cr(VI ) concentration. Langmuir and Freundlich adsorption

isotherm models were applied to analyze adsorption data, and both were found to be

applicable to this adsorption system, in terms of relatively high regression values.

Thermodynamic parameters showed that the adsorption of Cr(VI) onto carbon slurry was

feasible, spontaneous and exothermic under studied conditions. Kinetics of adsorption

was found to follow pseudo second order rate equation. Column studies have been carried

out to compare these with the batch capacities. The recovery of Cr(VI) and chemical

regeneration of the spent column have also been tried. In all, the results indicated that the

adsorbent used in this work proved to be effective material for the treatment of chromium

bearing aqueous solutions.

Keywords: Carbon slurry; Hexavalent chromium; Adsorption isotherm models;

Thermodynamic parameters; Kinetics

ACCEPTED MANUSCRIPT

3

1. Introduction

Chromium is generated from various industrial processes like electroplating,

leather tanning, wood preservations, manufacturing of dye, paint and paper and

petroleum refining processes [1]. The effluents from these industries contain both Cr(VI)

and Cr(III) in concentrations ranging from tens to hundreds of milligram per liters.

However, hexavalent form is five hundred times more toxic than the trivalent one and

human toxicity of Cr(VI) includes skin irritation to lung cancer, as well as kidney, liver,

and gastric damage [2]. Because of these differences, the discharge of Cr(VI) to surface

water is regulated to below 0.05 mg/L by the U.S. EPA, while total Cr, including Cr(III),

Cr(VI), and its other forms, is regulated to below 2 mg/L [3].

The conventional chromium treatment method consists of four steps:

1. Reduction of Cr(VI) to Cr(III).

2. Precipitation of Cr(III) as Cr(OH)3 at high pH.

3. Settling of the insoluble metal hydroxide.

4. Disposal of the dewatered sludge.

Due to major shortcomings of conventional treatment methods including the high

cost of safely disposing the sludge, expensive chemicals necessary for Cr(VI) reduction,

and incomplete reduction of Cr(VI), adsorption processes are considered to be the

appropriate method. Adsorption, an effective and versatile method for removal of heavy

metals is when combined with suitable desorption step solves the problem of sludge

disposal [4]. A number of low cost adsorbents have been used earlier for the removal of

toxic pollutants from waste waters [5-10]. During recent years, among them various

naturally available adsorbents like wool, olive cake, sawdust, pine needles, almond shells,

ACCEPTED MANUSCRIPT

4

cactus leaves, charcoal used tyres, soot, hazelnut shell, coconut shell charcoal, banana

peel, seaweed, dead fungal biomass, cyanobacterium and green alga were used for

removal of chromium [11- 19]. However, many of these naturally available adsorbents

have low chromium adsorption capacity and slow process kinetics. Thus, there is the

need to develop innovative low cost adsorbents useful for both industries and

environment.

Since in India large numbers of fertilizer plants are working to produce

fertilizer, and they use oil as a fuel to generate energy. But, due to incomplete combustion

of fuel in generator, fertilizer plants produces large amount of solid waste product called

carbon slurry. This waste product also creates disposal management problem. In this

work efforts have been made to put this solid waste to use by converting it into a suitable

adsorbent material. Earlier researchers have reported on carbon slurry promising results

for the removal of dyes Vertigo Blue 49, and Orange DNA 13, chlorophenols, fluoride,

and of pesticides [20-23]. Use of carbon slurry has also been reported for some metal ions

viz. on Hg2+, Pb2+ and Cu2+ [24, 25], but still there is lots of scope available to use this

waste, carbon slurry, for the removal of other heavy metal ions from waste waters. In the

same sequence in this investigation, adsorption studies for the removal of hexavalent

chromium from aqueous solutions by carbon slurry are carried out.

2. Materials and Methods

Fertilizer plants in India generate large amounts of carbon slurry waste due to

incomplete combustion of oil fuel. This slurry is stored in large tanks and allowed to dry.

The dried cake material, available at very cheap rate, was procured from National

ACCEPTED MANUSCRIPT

5

Fertilizer Limited, Panipat (India) and powdered. It was found to consist of small, black

and greasy granules form. Raw material obtained from plant was initially hydrophobic in

nature but when activation performed it will be changed into hydrophilic.

All reagents used were of AR grade either from Merck, Germany or SD Fine

Chem. Ltd., India and solutions were prepared using Milli-Q water. Standard solution of

Cr(VI) (1000 mg/L) for atomic adsorption spectrometry was obtained from Merck,

Germany. To adjust the pH, 0.1 N HCl and 0.1N NaOH solutions were used and 30% w/v

analytical grade H2O2 manufactured by S.D. Fine, India, was used to activate carbon

slurry. HNO3 utilized in column studies was supplied by Merck, Delhi, India.

2.1. Equipment

The pH measurements were made using a pH meter (model cyber scan 510,

Singapore). The chromium solutions were analyzed using an atomic adsorption

spectrophotometer model Z- 7000 (Hitachi, Japan) at a wavelength of 357.9 nm. LEO

435 VP (Leo Elektronenmikroskopie GmbH, Germany), scanning electron microscopy

was used for the scanning of carbon slurry. Infra red spectra of the samples were recorded

on a FTIR, Spectrophotometer model –1600, (Perkin Elmer, USA).

2.2. Preparation of adsorbent

The raw material was obtained in the form of small, spherical carbonaceous,

black, greasy granules from the fertilizer industries. Firstly, it was powdered and treated

with hydrogen peroxide for 24h at room temperature to oxidize the adhering organic

material, and then heated to 473 K in air until the emission of black soot was completely

stopped. Now material was cooled and activated in muffle furnace for 2h at 723 K in the

presence of air. The activated product obtained was about ~90% which is further treated

ACCEPTED MANUSCRIPT

6

with 1.0M HCl solution to remove remaining ash content and then washed with doubled

distilled water, thereafter it was dried in an oven at 373 K, 24h. The dried product is

referred to as carbonaceous adsorbent and was sieved to obtain different particles sizes

corresponding to 100-150, 150-200 and 200-250 British Standard Sieve (BSS) mesh and

stored in vacuum desiccators.

2.3. Batch adsorption studies

. Adsorption was determined by batch method, which permits convenient

evaluation of parameters that influence the adsorption process. In batch method, a fixed

quantity of carbon slurry is mixed continuously with a specific volume of solution or

waste and constantly agitated at 303±2 K, until the equilibrium was reached. At the end

of adsorption, 1 ml sample was collected and centrifuged at 1500 rpm for 10 min. on a

centrifuge. The filtrate was collected in polythene tubes and diluted before analysis. The

concentration of remaining Cr(VI) ions in the adsorption medium was determined using

an atomic adsorption spectrophotometer model Z- 7000 (Hitachi, Japan) at a wavelength

of 357.9 nm. Before determination of the total quantity of chromium Cr(VI) in the

adsorption medium, Cr3+ and Cr2+ were converted to Cr(VI) using KMnO4. The

adsorption capacities were then obtained by mass balance calculations.

For adsorption isotherms, a series of 25 ml glass tubes were filled with 10 ml

Cr(VI) solution of varying concentrations (10-100 mg/L), maintained at desired

temperature and pH. Then equal amount of activated carbon slurry was added into each

test tube. The amount of carbon slurry used for Cr(VI) solutions was 4.0 g/L, after the

optimum uptake time (70 min) the concentrations of chromium ion was calculated by

taking the difference in their initial and final concentrations. In each experiment constant

ACCEPTED MANUSCRIPT

7

shaking of the solution was performed by using magnetic stirrer. All the experiments

were repeated three times and average values were reported. The standard deviation was

found to be ±1.8%.

Kinetic studies of adsorption by fertilizer waste were also carried out at two

initial chromium concentrations (50 and 100 mg/L) at 303 K wherein the extent of

adsorption was analyzed at regular time interval.

2.4. Column studies

Adsorption isotherms are used for some primary studies and obtaining the

operational parameters before running more costly experiments. Hence, the practical

applicability of the product for column operations has also been studied to obtain some

parameters necessary for a factual design model. A glass column (30 × 1.5 cm) filled

with a known amount of carbon slurry (mesh size 100-150 B.S.S.) was used. Effluent

flow was adjusted with a clip at the bottom of the column. The column runs were carried

out up to the point where the break through capacity was consumed.

2.5. Regeneration

Regeneration of adsorbent as well as recovery of adsorbate material is quite

important, therefore, the same have been achieved by using 1% HNO3. For this the

desorption studies were conducted using different desorbing agents like 1% HNO3, HCl,

0.3 M NH4OH, NaCl and deionized H2O. The adsorbent loaded with Cr(VI) metal ion

was placed in the desorbing medium and was constantly stirred on a rotatory shaker at

100 rpm for an hour at 303 K. Desorption ratio is given as the amount of metal ions

desorbed to the amount of metal ions adsorbed multiplied by 100. Simultaneous

regeneration of adsorbent was also tried.

ACCEPTED MANUSCRIPT

8

3. Results and discussion

3.1. Characterization of the prepared adsorbent

The carbon slurry was chemically analyzed and it was found to be organic in

nature; i.e., it contains constituents such as carbon (78.93%), oxygen (19.41%), Al

(1.16%), and F (0.49%). Carbon (due to the presence of coke particles) is the prominent

component of carbon slurry. The organic content generally imparts porosity to the

adsorbent as observed in the SEM results which is highly porous in nature (fig.1). This is

reflected in the surface area of the adsorbents which were found to be 388 m2/g

(calculated by our laboratory workers) for carbonaceous adsorbent, as the carbon content

decreases, the surface area correspondingly decreases [26,27]. On the basis of surface

area, the carbonaceous adsorbent is expected to be a useful material for the removal of

metal ions.

FIGURE 1

The samples of carbonaceous adsorbent was stirred with deionized water for 2 h

and left for 24 h to see any interaction. It was seen that in carbonaceous adsorbent, the pH

of water was lowered, which indicates it as carbonaceous adsorbent as per Steenberg

classification [28] comes under “L” type carbon. IR spectrum of the sample of

carbonaceous adsorbent taken indicates the presence of two prominent bands lying at

1634 and 3420 cm-1 . The first peak may be assigned to the presence of a carbonyl group,

and the latter one may be assigned to the presence of the OH group.

ACCEPTED MANUSCRIPT

9

3.2. Adsorption studies

Adsorption of Cr(VI) on a low cost fertilizer industry waste material, carbon

slurry, was studied as a function of pH, temperature, dose, metal ion concentration and

adsorbent particle size. The adsorption data were fitted to different isotherms.

3.2.1. Effect of pH

Hexavalent chromium removal by the fertilizer waste at 303 K temperature and an

initial calculated metal ion concentration of 50 and 100 mg/L was found to be pH-

dependent as shown in fig 2. Equilibrium chromium sorption was favoured by acidic pH

range of 1-3 and maximum adsorption by the carbon slurry was observed at pH 2.0. Thus,

the results showed that the uptake of Cr(VI) rises from 8.5 (pH 1.0) to 14.8 mg/g (pH 2.0)

and then starts to decrease. Accordingly, the optimum pH for the maximum uptake of

Cr(VI) was found at 2.0.

Figure 2

This could be explained that since Cr(VI) exists in the form of oxyanions such

as HCrO4−, Cr2O7

2−, CrO42−, etc. in acidic medium and the lowering of pH causes the

surface of the adsorbent to be protonated to a higher extent and as a result a strong

attraction exists between these oxyanions of Cr (VI) and positively charged surface of the

adsorbent. Hence, the uptake increases with increasing pH from 1.0 to 2.0 of the solution.

Whereas at high pH there will be abundance of negatively charged hydroxyl ions in

aqueous solution, causing hindrance between negatively charged ions Cr2O72−, CrO4

2−,

etc and negatively charged adsorbent, resulting in decrease of adsorption.

ACCEPTED MANUSCRIPT

10

Thus during adsorption of Cr(VI) on the surface of carbon slurry there was

adsorption of Cr(VI) as well as Cr(III). Reduction of Cr(VI) into Cr(III) is also clear from

the aqueous chemistry of Cr(VI) at low pH value:

Cr2O72- + 6e- + 14 H+ ���� Cr3+ + 7H2O E0 = 1.3V (1)

For the determination of Cr(VI), its supernatant was separated from the reaction mixture

and divided into two parts. In one part equilibrium concentration of the Cr(VI) was

measured by prescribed method. Whereas second part was heated up to 125-140 °C with

powerful oxidizing reagent such as KMnO4. The concentration of Cr(VI) is then

measured, which shows higher equilibrium concentration. Reason is that, KMnO4 oxidize

all the Cr(III) into Cr(VI), present in the solution, which was formed at the surface of

carbon slurry during the adsorption process at very low pH. Similar type of observation

was also reported by some other workers [29,30].

3.2.2. Effect of contact time

Fig. 3 shows the comparative data of the effect of contact time on the extent of

adsorption of Cr(VI) on the carbon slurry at 50 and 100 mg/L initial chromium

concentration at pH 2.0 and temperature 303 K. It has been observed that the metal

adsorption rate is high at the beginning and then decreases slowly till saturation levels

were completely reached at equilibration point (70 min.). The data obtained from this

experiment were further used successfully to evaluate the kinetics of the adsorption

process.

Figure 3

3.2.3. Effect of particle size

ACCEPTED MANUSCRIPT

11

The adsorption of Cr(VI) on carbon slurry at pH 2, and 100mg/L was

investigated at three particle sizes, 100–150, 150–200, and 200–250 mesh, respectively,

as shown in fig. 4. It was found that the adsorption capacity increases with decrease in

particle size of the adsorbent as there is increase in surface area. But it may be possible

that Cr(VI) ion are not able to penetrate to some of the interior pores of the particles,

especially when their sizes are large. The access to all pores is facilitated in small size

particles. Similar results were also obtained by McKay et. al. [31]. Particles size 100-150

mesh show maximum adsorption capacity.

Figure 4

3.2.4. Effect of adsorbent dose

To determine the effect of adsorbent dose, different amounts (1-10 mg/L) of

adsorbent was suspended in 10 ml chromium solution in which the concentration of

chromium was 100 mg/L under optimized conditions of pH and contact time. The effect

of adsorbent dose on the amount of chromium (VI) adsorbed in mg/g and extent of

removal of chromium for the adsorbent is shown in fig. 5. The amount of adsorbent

significantly influenced the extent of chromium (VI) adsorption. The extent of Cr(VI)

removal was found to be 3% for 0.5 g/L of adsorbent. It greatly increased to 65% for 4

g/L of adsorbent, respectively. However, it has been observed that there was only a slow

change in the extent of Cr(VI) adsorption for carbon slurry, when the adsorbent dose was

over 4 g/L. Furthermore, higher adsorbent dose result in lower adsorption capacity ( qe =2

mg/g at 1 g/L dose for carbon slurry) value at a fixed Cr(VI) concentration (100 mg/L)

as shown in fig. 5. At low dose, all types of sites are entirely exposed and the adsorption

ACCEPTED MANUSCRIPT

12

on the surface is saturated faster, showing a higher qe value. But at higher adsorbent dose,

the availability of higher energy sites decreases with a larger fraction of lower energy

sites occupied, resulting in a lower qe value. Thus, an optimum dose of 4g/L is selected

for all the experiments. Similar type of result has also been observed by other researchers

also [14,15].

Figure 5

3.2.5. Effect of Cr(VI) concentration

The effect of Cr(VI) concentration on carbon slurry was investigated at different

chromium concentrated solutions and results are shown in fig. 6. This plot show that the

time for equilibrium adsorption remains unchanged, and shows maximum adsorption at

100mg/L. Similar type of observations were obtained while studying the adsorption of

dyes [32].

Figure 6

3.3. Adsorption Isotherm Modelling

Temperature effect experiments were performed at pH 2.0, initial Cr(VI)

concentration 100mg/L, 0.4g adsorbent and at various temperatures of 303, 313 and 323

K. It was observed that the uptake (mg/g) of chromium ion decreases from 14.7, 13.8 to

12.8 with the rise in temperature from 303, 313 to 323 K (fig. 7). This result also shows

that the adsorption was exothermic in nature.

Figure 7

The results obtained from adsorption isotherms were analyzed with Langmuir

and Freundlich models as discussed earlier [12]. The plots of 1/qe vs 1/Ce (Langmuir plot)

and ln qe vs ln Ce (Freundlich plot) [figures not shown] were drawn at three different

temperatures and the Langmuir and Freundlich adsorption constants and the regression

ACCEPTED MANUSCRIPT

13

correlation coefficient obtained are given in Table 1. The values of regression

coefficients obtained from these models were used as the fitting criteria to find out these

isotherms. It was found that both the plots depicted the linearized form of the isotherms at

all temperatures and the extremely high correlation coefficients (R2 = 0.98,0.99), thus

indicating both monolayer and heterogenous surface conditions. Also, from the Langmuir

adsorption constant qe, the adsorption capacity of Cr(VI) on carbon slurry was observed

as 15.24 mg/g at 303 K which decreased with the increase in temperature. When

compared with several other low cost adsorbents, the present low cost adsorbent from

fertilizer waste i.e. carbon slurry was found to show comparable hexavalent chromium

adsorption (15.24 mg/g).

3.4. Thermodynamic study

To study the thermodynamics of adsorption of Cr(VI) on low cost adsorbent

carbon slurry, thermodynamic constants such as enthalpy change ∆H°, free energy change

∆Go and entropy change So were calculated using equations described in our earlier

work [18]. The values of these parameters are given in Table 2. A perusal of Table 2

indicated that the enthalpy change ∆H° is negative (exothermic) due to decrease in

adsorption on successive increase in temperature. Further, negative ∆Go values indicate

thermodynamically feasible and spontaneous nature of the adsorption process and

positive value of So reveals the increased randomness at the solid-solution interface

during the fixation of the Cr(VI) on the active sites of the adsorbent.

3.5. Kinetic study

ACCEPTED MANUSCRIPT

14

The mathematical representations of Pseudo first- and second- order kinetic

models are given in equation 2 and 3.

log ( qe - qt ) = log qe – 2.303k ads 1, t (2)

tqqkq

t

eeads

112

,2

+= (3)

where qe the equilibrium sorption uptake at time t = infinity and qt (mg/g) is the

amount of adsorbed chromium on the adsorbent at time t and k1,ads (/min) and k2,ads (g/

mg/min) are the rate constant of first-order and second order adsorption. The adsorption

rate constant (k1) for chromium sorption was calculated from the slope of the linear plot

of ln (qe-qt) versus time. In the latter case, kinetic data were plotted between t/qt against t

as shown in fig. 8. The kinetic rate constants obtained from first and second-order pseudo

kinetic model are given in Table 3. The values of correlation coefficient R2 for the

pseudo-second-order adsorption model is relatively high (>0.9979), and the adsorption

capacities calculated by the model are also close to those determined by experiments.

However, the values of R2 for the pseudo-first-order are not satisfactory. Therefore, it has

been concluded that the pseudo-second-order adsorption model is more suitable to

describe the adsorption kinetics of chromium ion on carbon slurry.

Figure 8

3.6. Comparison with other adsorbents

Table 4 compares maximum adsorption capacities obtained in this study with

some other values reported in the literature. The adsorption capacity for chromium using

carbon slurry, a waste from the fertilizer industry, is of the same order of magnitude or

greater than that has been found using similar adsorbents [33- 37].

ACCEPTED MANUSCRIPT

15

3.7. Column studies

The results obtained from adsorption batch experiments were used to remove

chromium metal ion by column. The flow rate was varied to achieve the maximum

removal of the adsorbate and it was found that the maximum uptake of chromium was

achieved at flow rate 1.0 ml/min. About 92–93% chromium is removed at lower flow

rates (1.0 ml/ min), while this decreases with increased flow rate. The plots of C/Co

versus time or volume, for a constant flow rate, depict the increase in the ratio of effluent

to influent concentration as the zone moves through the column.

The breakpoint on the curve has been adopted by various workers differently to

determine the breakthrough capacity of the column [38, 39]. The calculation [29] of

breakthrough capacity, exhaustion capacity and degree of column utilization have been

evaluated from breakthrough curve as given in fig. 9 was found to be 28.0 mg/g for

chromium, which is greater than in the batch experiments (15.24 mg/g). The high column

capacity may be due to the fact that a continuously large concentration gradient occurred

at the interface zones as it passes through the column, while the concentration gradient

decreased with time in the batch experiments.

Figure 9

Regeneration and recovery of the column is a very important aspect in wastewater

treatment processes and, therefore, desorption of chromium was tried with a number of

eluents like, deionized water, ammonium hydroxide, sodium chloride, hydrochloric acid,

nitric acid, etc. and it was found that the desorption of the metal ion occurred by 1%

HNO3. The column was allowed to pass 1 % HNO3 at a flow rate of 1.0 ml/min for about

2 h and then again allowed to pass deionized water at the same flow rate. It was observed

ACCEPTED MANUSCRIPT

16

that the column loses about 3% capacity after the first run and about 10–15% after more

than five runs. Therefore, the column can be used for at least five runs without any

problem. It is very important to mention here that carbon slurry, a waste from fertilizer

industry, is an easily available, inexpensive material, and its cost is very low in

comparison to the cost of regeneration.

4. Summary

The batch studies conducted in the present study provides significant information

regarding adsorption of chromium on carbon slurry in terms of optimum pH and

adsorbent dose for maximum removal of Cr(VI) from the aqueous solution. The studies

indicate that carbon slurry is an effective adsorbent for Cr(VI) removal. The maximum

Cr(VI) adsorption capacity has been found to be 15.244 mg/g Cr(VI) of dry weight of

adsorbent at an carbon slurry dose of 4.0 g/L in 70 min. of contact time with initial

Cr(VI) concentration of 100 mg/L, 303 K temperature and optimum pH of 2.0. The

Langmuir and Freundlich adsorption model were used for the mathematical description

of the adsorption of Cr(VI) ions onto carbon slurry and it was found that the adsorption

equilibrium data fitted well to both the models. The adsorption of chromium ions on the

carbon slurry follows second order adsorption kinetics and 5% HNO3 efficiently desorbed

metal from the metal-loaded adsorbent. The studies on column operations show that the

product can also be used on an industrial scale. Metal ions adsorbed on the column of this

material can be quantitatively eluted with HNO3 .The exhausted column can be

chemically regenerated by treating it with HNO3 and no dismantling is required. Other

salts present in effluents do not cause any disturbing effects. The advantage of high metal

adsorption capacity, proves that the carbon slurry has the potential to be used as an

ACCEPTED MANUSCRIPT

17

efficient and economic adsorbent material for the removal of chromium from aqueous

phase.

ACKNOWLEDGEMENT

One of the authors, Arunima Nayak, is thankful to Ministry of Human Resource

Development (MHRD), New Delhi, India, for financial support.

References

ACCEPTED MANUSCRIPT

18

[1] L. Khezami, R. Capart, Removal of chromium(VI) form aqueous solution by

activated carbons: kinetic and equilibrium studies, J. Hazard. Mater. 123 (2005) 223–

231.

[2] US Department of Health and Human Services, Toxicological Profile for Chromium.

Public Health Service Agency for Toxic substances and Diseases Registry, Washington,

DC, 1991.

[3] World Health Organization (WHO), Guidelines for Drinking-water Quality, Vol:1,

3rd ed., Recommendations, Geneva, 2004, pp. 334.

[4] S.E. Bailey, T.J. Olin, R.M. Bricka, D.D. Adrian, A review of potentially low-cost

sorbents for heavy metals, Water Res. 33 (1999) 2469–2479.

[5] A. Mittal, L. Kurup, V.K.Gupta, Use of waste materials- Bottom ash and De-Oiled

soya as potential adsorbents for the removal of Amaranth from aqueous solutions, J.

Hazard. Mater. 117 (2005) 171-178.

[6] V.K. Gupta, I. Ali, Suhas, V.K. Saini,�Removal of chlorophenols from wastewater

using red mud: An aluminum industry waste, Environ. Sci. Tech. 38 (2004) 4012-4018.

[7] V.K. Gupta, S. Sharma, Removal of zinc from aqueous solutions using bagasse fly

ash – a low cost adsorbent, Indust. Eng. Chem. Res. 42 (2003) 6619-6624.

[8] V.K.Gupta, C.K. Jain, I. Ali, S. Chandra, Removal of lindane and malathion from

wastewater using bagasse fly ash - A sugar industry waste, Water Res. 36 (2002) 2483-

2490.

[9] V.K.Gupta, S.K.Srivastava, R. Tyagi, Design parameters for the treatment of phenolic

wastes by carbon columns (obtained from fertilizer waste material), Water Res. 34

(2000) 1543- 1550.

ACCEPTED MANUSCRIPT

19

[10] V.K. Gupta, A. Rastogi, M.K. Dwivedi, D. Mohan, Process development for the

removal of zinc and cadmium from wastewater using slag – A blast furnace waste

material, Sep. Sci. Techol., 32 (1997) 2883-2912.

[11] J. Lakatos, S.D. Brown, C.E. Snape, Coals as sorbents for the removal and reduction

of hexavalent chromium from aqueous waste streams, Fuel 81 (2002) 691–698.

[12] N.K. Hamadi, X.D. Chen, M.M. Farid, M.G.Q. Lu, Adsorption kinetics for the

removal of chromium (VI) from aqueous solution by adsorbents derived from used tyres

and sawdust, Chem. Eng. J. 84 (2001) 95–105.

[13] S.H. Hasan, K.K. Singh, O. Prakash, M. Talat, Y.S. Ho, Removal of Cr(VI) from

aqueous solutions using agricultural waste ‘maize bran’, J. Hazard. Mater. 152 (2008)

356-365.

[14] D. Park, Y.S. Yun, J.M. Park, Use of dead fungal biomass for the detoxification of

hexavalent chromium: screening and kinetics, Process Biochem. 40 (2005) 2559–2565.

[15] M. Kobya, Adsorption, kinetic and equilibrium studies of Cr (VI) by hazelnut shell

activated carbon, Adsorp. Sci. Technol. 22 (2004) 51–64.

[16] J. R. Memona, S. Q. Memonb, M.I. Bhangera, A. El-Turkic, K. R. Hallamc, G. C.

Allenc, Banana peel: A green and economical sorbent for the selective removal of Cr(VI)

from industrial wastewater, Colloid Surfaces B: Biointer. 70 (2009) 232–237.

[17] Z. A. Zakaria, M. Suratman, N. Mohammed, W.A. Ahmad, Chromium(VI) removal

from aqueous solution by untreated rubber wood sawdust, Desalin. 244 (2009) 109–121.

[18] V.K.Gupta, A.Rastogi, Sorption and desorption studies of chromium(VI) from

nonviable cyanobacterium Nostoc muscorum, J. Hazard. Mater. 154 (2008) 347-354.

ACCEPTED MANUSCRIPT

20

[19] V.K.Gupta, A.Rastogi, Biosorption of hexavalent chromium(VI) by raw and acid

treated green alga Oedogonium hatei from aqueous solutions, J. Hazard. Mater. 163

(2009) 396-402.

[20] V.K. Gupta, I. Ali, V.K. Saini, adsorption studies on the removal of Vertigo Blue 49

and DNA13 from aqueous solution using carbon slurry developed from a waste material,

J. Colloid. Interf. Sci. 315 (2007) 87-93.

[21] A.K. Jain, V.K. Gupta, S. Jain, and Suhas, Removal of chlorophenols using

industrial waste, Environ. Sci. Technol. 38 (2004) 1195-1200.

[22] V.K. Gupta, I. Ali, V. K. Saini, Defluoridation of waste using waste carbon slurry,

Water Res. 41 (2007) 3307-3316.

[23] V.K. Gupta, I. Ali, Suhas, V.K. Saini, Adsorption of 2, 4-D and carbofuran

pesticides using fertilizer and steel industry wastes, J. Colloid. Interf. Sci. 299 (2006)

556-563.

[24] D. Mohan, V. K. Gupta, S.K. Srivastava, S. Chander, Kinetics of mercury adsorption

from wastewater using activated carbon derived from fertilizer waste, Colloid. Surf. A;

Physiochem. Eng. aspects 177 (2001) 169-181.

[25] V.K. Gupta, S.K. Srivastava, D. Mohan, S. Sharma, Design parameters for fixed bed

reactors of activated carbon developed from fertilizer waste for the removal of some

heavy metal ions, Waste Management 17 (1997) 517–522.

[26] N. Daneshvar, D. Salari, S. Aber, Chromium adsorption and Cr (VI) reduction to

trivalent chromium in aqueous solutions by soya cake, J. Hazard. Mater. B94 (2002) 49–

61.

ACCEPTED MANUSCRIPT

21

[27] E.I. El-Shafey, Behavior of reduction-sorption of chromium (VI) from an aqueous

solution on a modified sorbent from Rice Husk, Water air and soil pollution 163 (2005)

81–102.

[2822] J.S. Mattson, H. B. Mark, Jr. Activated Carbon Surface Chemistry and

Adsorption from Solution; Marcel Dekker: New York, 1971.

[29] F.W. Pontius, Water Quality and Treatment, fourth ed., McGraw-Hill, New York,

1990.

[30] Q.L. Diana, M. Oliveira, L.C.A. Gonçalves, Luiz Oliveria, R.G. Guilherme,

Removal of As(V) and Cr(VI) from aqueous solutions using solid waste from leather

industry, J. Hazard. Mater., 151 (2008) 280-284.

[31] G. McKay, M.S. Otterburn, A.G. Sweeny, The removal of colour from effluent

using various adsorbents –IV Silica: Equilibria and column studies, Water Res. 14 (1980)

21-27.

[32] A. Bhatnagar, A.K. Jain, A comparative adsorption study with different industrial

wastes as adsorbents for the removal of cationic dyes from water, J. Colloid Interface

Sci. 281 (2005) 49–55.

[33] H. Gao, Y. Liu, G. Zeng,W. Xu, T. Li,W. Xia, Characterization of Cr(VI) removal

from aqueous solutions by a surplus agricultural waste - Rice straw, J. Hazard. Mater.

150 (2008) 446-452.

[34] U.K. Garg, M.P. Kaur, V.K. Garg, D. Suda, Removal of hexavalent waste from

aqueous solutions by agricultural waste biomass, J. Hazard. Mater. 140 (2007) 60-68.

ACCEPTED MANUSCRIPT

22

[35] M. Dakiky, M. Khamis, A. Manassara, M. Mer’eb, Selective adsorption of

chromium (VI) in industrial wastewater using low-cost abundantly available adsorbents,

Adv. Environ. Res. 6 (2002) 533–540.

[36] V.K. Gupta, I. Ali, Removal of lead and chromium from wastewater using bagasse

fly ash – a sugar industry waste, J. Colloid Interface Sci. 271 (2004) 321-328.

[37] V.K.Gupta, M.Gupta, S.Sharma, Process development for the removal of lead and

chromium from aqueous solutions using red mud- an aluminium industry waste, 35

(2001) 1125-1134.

[38] C.J. N.loutier, A.Leduy, R.S.Ramalho, Peat adsorption of herbicide 2,4-D from

wastewaters, Can. J. Chem. Eng., 63 (1985) 250-257.

[39] A.H. Mollah, C.W. Robinson, Pentachlorophenol adsorption and desorption

characteristics of granular activated carbon – II. Kinetics, Water Res., 30 (1996) 2907-

2913.

ACCEPTED MANUSCRIPT

23

Table 1.

Langmuir and Freundlich isotherm constants for the adsorption of Cr(VI) on carbon

slurry at different temperatures and pH 2.0.

Langmuir constant Freundlich constant

b qe R2 KF R2 Temp

(K) (L/mg) (mg/g)

n (mg/g) `

303 0.0024 15.24 0.985 1.534 1.091 0.99

313 0.0051 6.14 0.99 1.453 1.024 0.99

323 0.0054 5.08 0.99 1.518 1.022 0.98

ACCEPTED MANUSCRIPT

24

Table2.

Thermodynamic parameters for the adsorption of Cr(VI) on carbon slurry at different

temperatures.

Temp

(K)

� G°

(kJ/mol)

� S°

(kJ/mol K)

� H° *

(kJ/ mol)

303 -14.183 0.063

313 -14.534 0.060

323 -13.005 0.063

-33.244

*Measured between 303 and 323 K.

ACCEPTED MANUSCRIPT

25

Table 3.

Adsorption rate constants, qe estimated and coefficient of correlation associated to the

Lagergren pseudo-first and second order adsorption for the carbon slurry (pH 2.0).

First –order model Second-order model

Initial

conc.

(mg/L)

qe exp.

(mg/ g)

k1 ( × 10-3

min-1)

qecal..

(mg/g)

R2

k2 ( × 10-3

g/mg/min)

qecal.

(mg/g)

R2

50 7.8 42.14 6.567 0.979 13.155 8.123 0.997

100 15.2 49.51 11.34 0.959 6.787 16.287 0.998

ACCEPTED MANUSCRIPT

26

Table 4.

Comparison of adsorption capacities of Cr(VI) onto carbon slurry with different sorbents.

Adsorbent Adsorbent capacity (mg/g) Reference

Rice straw 3.15 [33]

Maize Corn cob 0.28 [34]

Jatropha oil cake 0.82 [34]

Sugarcane bagasse 0.63 [34]

Sawdust 15.84 [35]

Olive cake 33.4 [35]

Pine needles 21.5 [35]

Almond 10.62 [35]

Coal 6.78 [25]

Cactus leaves 7.08 [35]

Bagasse fly ash 4.35 [36]

Red mud 4.36 [37]

Carbon slurry 15.24 This study

FIGURE CAPTIONS:

ACCEPTED MANUSCRIPT

27

Fig.1. SEM photographs of carbon slurry at different magnifications (a) 5000X, (b)

3500X, (c) 2000X and (d) 250X

Fig 2. Effect of pH on the adsorption of Cr(VI) on the carbon slurry, pH 1.0–7.0; initial

Cr(VI) concentration 50 and 100 mg/L; adsorbent dose 4.0 g/L, temperature 303 K and

particle size 100-150 mesh.

Fig.3. Effect of contact time on the adsorption of Cr(VI) on the carbon slurry, at pH 2.0,

initial Cr(VI) concentration 50 and 100 mg/L, adsorbent dose 4.0 g/L and particle size

100-150 mesh.

Fig.4. Effect of particle size of the carbon slurry on the adsorption of Cr(VI), at pH 2.0,

initial Cr(VI) concentration 100 mg/L, adsorbent dose 4.0 g/L and temperature 303 K.

Fig.5. Effect of adsorbent dosage on the uptake of Cr(VI) on carbon slurry at pH 2.0, 100

mg/L Cr(VI) concentration and temperature 303 K.

Fig: 6. Effect of Cr(VI) concentration on it’s adsorption on carbon slurry at 303 K, 4.0g/L

dose.

Fig. 7 Adsorption isotherms of chromium at different temperatures.

Fig. 8. Second-order kinetic modeling of Cr(VI) ions adsorption on carbon slurry.

Fig. 9. Breakthrough curve of Cr(VI) on activated carbon slurry.

ACCEPTED MANUSCRIPT

28

Fig.1. SEM photographs of carbon slurry at different magnifications (a) 5000X, (b)

3500X, (c) 2000X and (d) 250X

ACCEPTED MANUSCRIPT

29

Fig 2. Effect of pH on the adsorption of Cr(VI) on the carbon slurry, pH 1.0–7.0; initial

Cr(VI) concentration 50 and 100 mg/L; adsorbent dose 4.0 g/L, temperature 303 K and

particle size 100-150 mesh

1.12 2.08 3.11 4.03 5.15 6.05 7.16

50 mg/L

0

24

68

10

12

14

16

Am ount adsorbed (m g/g)

pH

50 mg/L

100 mg/L

ACCEPTED MANUSCRIPT

30

Fig.3. Effect of contact time on the adsorption of Cr(VI) on the carbon slurry, at pH 2.0,

initial Cr(VI) concentration 50 and 100 mg/L, adsorbent dose 4.0 g/L and particle size

100-150 mesh.

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100 120 140Time(min.)

Am

ount

ads

orbe

d m

g/g

50 ppm

100 ppm

ACCEPTED MANUSCRIPT

31

\

Fig.4. Effect of particle size of the carbon slurry on the adsorption of Cr(VI), at pH 2.0,

initial Cr(VI) concentration 100 mg/L, adsorbent dose 4.0 g/L and temperature 303 K.

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100 120 140Time (min.)

Am

ount

ads

orbe

d m

g/g

100-150 m esh

150-200 m esh

200-250 m esh

ACCEPTED MANUSCRIPT

32

Fig.5. Effect of adsorbent dosage on the uptake of Cr(VI) on carbon slurry at pH 2.0, 100

mg/L Cr(VI) concentration and temperature 303 K.

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6Adsorbent dose (g/L)

Ads

orpt

ion

capa

city

qe

(mg/

g)

0

20

40

60

80

100

Ads

orpt

ion

exte

nt (%

)

"ads .capacity ads .extent

ACCEPTED MANUSCRIPT

33

Fig: 6. Effect of Cr(VI) concentration on it’s adsorption on carbon slurry at 303 K, 4.0

g/L dose.

0

2

4

6

8

10

12

14

16

18

0 50 100 150Initial conc.mg/L

Am

ount

ads

orbe

d m

g/g

CHROMIUM

ACCEPTED MANUSCRIPT

34

Fig. 7 Adsorption isotherms of chromium at different temperatures.

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120 140Ce (mg/L)

Am

ount

ads

orbe

d m

g/g

303 K

313 K

323 K

ACCEPTED MANUSCRIPT

35

Fig. 8. Second-order kinetic modeling of Cr(VI) ions adsorption on carbon slurry.

second order

y = 0.1231x + 1.152

R2 = 0.9971

y = 0.0614x + 0.5554

R2 = 0.9979

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100 120 140

t (min)

t/qt

50 ppm

100 ppm

ACCEPTED MANUSCRIPT

36

Fig 9. Breakthrough curve of Cr(VI) on activated carbon slurry.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250 300volum e of e ffluent (m l)

Co

/Ci

chrom ium

ACCEPTED MANUSCRIPT

37

Graphical abstract

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100 120 140Time (min.)

Am

ount

ads

orbe

d m

g/g

100-150 m esh

150-200 m esh

200-250 m esh

Effect of particle size of the carbon slurry on the adsorption of Cr(VI)